Pistons used in internal combustion engines, and particularly in medium range diesel engines, are generally of one of three designs: gravity cast aluminum pistons, squeeze-formed aluminum/metal matrix composite pistons, and two-piece steel crown/aluminum skirt articulated pistons. There are fairly well defined levels of specific power output which each of these design options can tolerate. Cost varies greatly between the three designs, with gravity cast pistons being the most economical to manufacture.
Pistons encounter extreme thermal conditions and mechanical forces which together subject certain portions of the pistons to stress that can lead to deterioration and failure. To date, efforts have been taken to reinforce and/or thermally insulate portions of cast pistons so that they are more durable and have a longer service life. Such efforts include the design of a variety of insert structures which provide thermal barriers and/or internal structural supports. Examples of insert structures used in cast pistons are found in U.S. Pat. No. 5,425,306 to Binford, U.S. Pat. No. 4,971,003 to Suzuki et al., U.S. Pat. No. 4,890,543 to Kudou et al., U.S. Pat. No. 4,662,326 to Kohnert, U.S. Pat. No. 4,658,706 to Sander et al., U.S. Pat. No. 4,494,501 to Ludovico, U.S. Pat. No. 4,120,081 to Rosch et al., U.S. Pat. No. 2,685,729 to Daub, U.S. Pat. No. 2,473,254 to Morris, and U.S. Pat. No. 1,759,509 to Jardine.
Despite improvements made to cast pistons, they are generally inefficient. Accordingly, the trend toward stricter emissions requirements is rapidly rendering the use of conventional gravity cast pistons inadequate.